Touch panels are used in various fields such as portable computing devices (tablet, laptop PC, smartphone, cellular phone, PDA, etc.), digital audio players, portable game machines, car navigation devices, copiers, ATMs of financial institutions, and automatic ticket vending machines at stations and restaurants. Such a touch panel is operated by touching or pressing a desired position of a display surface, on which an image is displayed, with a finger or a dedicated pen called a touch pen, a stylus, or the like (hereinafter referred to as a “touch pen”).
There are available a resistive film touch panel, a surface acoustic wave touch panel, an infrared touch panel, an electromagnetic induction touch panel, a capacitive touch panel, and so on. Herein, in the capacitive touch panel, an input position on a display is detected by sensing a change in capacitance between a fingertip or a pen tip and a conductive film.
A touch pen for use with such a capacitive touch panel may be a passive pen or an active pen. In general, the passive pen mainly includes a pen holder and a pen tip made of a soft material such as a conductive rubber and attached to the tip of the pen holder.
On the other hand, the active pen mainly includes a pen holder, a pen tip attached to the tip of the pen holder, and an electric circuit provided in the pen holder and configured to generate an electric field from the pen tip. In the case of the active pen, since the electric field is generated from the pen tip, the position detection accuracy of the touch panel is relatively high so that the pen tip can be made thinner.
Recently, there has also been proposed a touch pen equipped with an erase function. When the erase function is installed in a rear end portion of the touch pen, and the rear end portion is of an active type, an electric circuit for the erase function is generally causing the touch pen to increase in both length and cost.